From a viewpoint of improving yield in fabrication of semiconductor devices, management of surface conditions of a peripheral portion of a substrate, such as a semiconductor wafer, has been attracting attention in recent years. In the fabrication process of the semiconductor devices, many materials are deposited on a silicon wafer to form a multilayer structure. Therefore, unwanted films and roughened surface are formed on a peripheral portion which is not used for products. It has been a recent trend to transport the substrate by holding only its peripheral portion using arms. Under such circumstances, the unwanted films remaining on the peripheral portion would be peeled off during various processes and could adhere to devices, causing lowered yield. Thus, a polishing apparatus for polishing the peripheral portion of the substrate has been used in order to remove the unwanted films and roughened surface therefrom.
An apparatus using a polishing tape as described in JP-A-2011-161625 for polishing the peripheral portion of the substrate is known as such a polishing apparatus. This type of polishing apparatus polishes the peripheral portion of the substrate by bringing a polishing surface of the polishing tape in sliding contact with the peripheral portion of the substrate. In this specification, the peripheral portion is defined as a region including a bevel portion which is the outermost portion of the substrate and a top edge portion and bottom edge portion located radially inwardly of the bevel portion.
FIG. 1A and FIG. 1B are enlarged cross-sectional views each showing a peripheral portion of a substrate. More specifically, FIG. 1A shows a cross-sectional view of a so-called straight-type substrate, and FIG. 1B shows a cross-sectional view of a so-called round-type substrate. In the substrate W1 shown in FIG. 1A, the bevel portion is a portion BB that is constituted by a top incline (a top bevel portion) PP, a bottom incline (a bottom bevel portion) Q1, and a side portion (an apex) RR, all of which form an outermost circumferential surface of the substrate W1. In the substrate W shown in FIG. 1B, the bevel portion is a portion BB having a curved cross section and forming an outermost circumferential surface of the substrate W1. The top edge portion is a flat portion E1 located radially inwardly of the bevel portion BB and located radially outwardly of a region D1 where devices are formed. The bottom edge portion is a flat portion E2 located opposite the top edge portion and located radially inwardly of the bevel portion BB. These top edge portion E1 and bottom edge portion E2 may be collectively referred to as near-edge portions.
In bevel polishing, a surface of a peripheral substrate portion is polished by pressing diamond polishing tape or the like, a polishing member, of a polisher against the surface, while rotating the substrate in a circumferential direction. For this reason, polishing conditions vary, in some cases, with the shape of the peripheral substrate portion before polishing.
To use the polishing tape, operators take measurements of a bevel portion before polishing and set up from experience a polishing condition (polishing recipe) that suit the bevel shape and check whether the polishing condition does not cause any problem, by actually polishing a substrate. Having made sure that there is no problem, the operators start processing several substrates continuously.
The shape of a bevel portion of a semiconductor wafer varies with its manufacturer. To ensure a stable supply of semiconductor wafers, semiconductor manufacturers sometimes purchase semiconductor wafers from several different semiconductor wafer manufacturers. In some cases, semiconductor manufacturers use semiconductor wafers of varying bevel shape, depending on the type of device. For this reason, semiconductor wafers running on a semiconductor-circuit production line vary in bevel shape from lot to lot or individually.
In such a case of wafers of varying bevel shape, considering a processing recipe every time the wafer shape changes gives much trouble to the operators who use the polishing apparatus, and results in an increase in downtime of the polishing apparatus.